Automatic volume control



Aug. 27, 1935. E. T. DICKEY 2,012,423

AUTOMATIC VOLUME CONTROL Filed Sept. 26, 1950 ummm EDWARD T. DI CKET M-[f-*C/i/ ATTORNEY Patented Aug. 27, 1935 NUNITED STATES mail PATENT OFFICE AUTOMATIC VOLUME CONTROL Edward T. Dickey, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application September 26, 1930, Serial No. 484,510 3 claims. (o1. 25o-2o) `for. example in phenomena known as swinging and fading.

Other possibilities causing such reception fluctuation may `reside in carrier amplitude decrease; structural shielding of loop antennae when the receiver is portable, as when installed in an automobile, and other similar phenomena sporadically varying the signal output of a receiver. As is well known, various arrangements have been proposed to minimize the iiuctuations in receiver output `already `referred to.

Now I have devised a novel and simple method of eliminating, or minimizing, the output signal variations in a radio receiver which ordinarily result from local iield variations and the other causes enumerated'. Briefly, variations in the strength of the incoming carrier wave are utilized to control the gain of the ampliiier stages so as to counteract the effect of the variations.

Accordingly, it is one-of the main objects of the present invention to control the gain of a high frequency amplifier by utilizing the steady component of the rectified output of the amplifier to regulate the amplification of the amplifier in such a sense that variations in the transmission medi'- um are effectively counteracted.

Another important object of the invention is to provide in a radio receiver, a device for giving 4automatic or semi-automatic control of signal volume, by utilizing the detector plate lcurrent in such a manner as to produce a varying bias potential on the control electrode of one, or more, of theampliiier tubes preceding the detector.

Another object of the invention is to provide a radio receiver provided with means for automatically minimizing effects due to incoming carrier wave `variations'byutilizing such variations to produce varying` voltage drops across an impedance disposed in the output circuit of the detector stage, and subsequently` using the aforementioned voltage variations to control the operation of the radio frequency amplifier stage, or

stages, in such a direction as to counteract the eiect of said carrier wave variations. Still other objects of the invention are to improve generally the simplicity and eiiiciency of l Y.

amplifier gain controls, and to particularly provide an automatic control device of signal volume in a radio receiver which is not only reliable in operation, but economically installed in a radio receiver.

The novel features which I believe to be charf acteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as toboth its organization and method of operation will best be understood by 1 reference to the following description taken in connection with the drawing in which I have indicated diagra-mmatically several circuit organizations whereby my invention may be carried'into effect.

In the drawing,

Fig. 1 diagrammatically shows a receiver circuit embodying the invention,

Fig. 2 diagrammatically shows a modification thereof,

Fig. 3 diagrammatically shows another modiiigrounded antenna circuit A, G is coupled, as at M, to the tuned input circuit of an electron dis charge tube l.l The input circuit of the tube is tuned by a Variable capacity` 2, while the output circuit of the tube is coupled, as at M1, to the tuned input circuit of a second electron discharge tube 3, the tuned input circuit of the second tube Vbeing tuned by a second variable condenser 4.

, The output circuit of the tube 3 is coupled, as at M2, to the tuned input circuit of a detector `stage embodying an electron discharge tube 6, k

type as shown but may be of the screen grid or indirectly heated cathode types if desired, are enerL` gized from a source of direct current B, the positive terminal of the source being connected to the primary coil of the coupling M2, and being connected to the primary coil of the coupling M1 through a lead 8. The negative terminal of the source B is connected to the oathodes of tubes l and twb'y a lead'g, it .being observed that both of these cathodes are-connected by a lead l@ to each other and to the cathode of the tube 6.

The control electrodes of tubes l and t arey connected by a lead l i to the positive terminal of-` 4former-M3, and the capacity ifi is shunted across from plate tocathode of tube to by-pass radio 4frequency current around the transformer pri- Vmary coil l. and thesource B1. ,derstood that detection is secured in the detec- -torzstage by 'means of the well known capacity It will be unand Ygrid leak arrangement l5 in the control .-electrodecircuit of the tube S.

As is Well known, the output of the detector Ystage is impressed, through the audio transformer vM3 uponasubsequent utilization means, the lat- Vv.ter beingof -anyyvell `known type such as subse- -quentgaudiof-amplication stages and/or a loud `speaker. To provide for the regulation of the Vgain control 4of the `present invention., there providedya lvariable resistance R connected between the'fnegative terminal of the source B1 .-and-thecathode `oi tube 6, a capacity C being shunted across the variable resistance R.

Since the detector anode current is in large V parta function vof the-'strength of the incoming carrier wave, at least for-'carriers of not too great strength,` the variation'in this anode current is utilized to produce varying Voltage drop -across the ohmicresistance R. This latter varying Voltage drop is utilized to produce .a varying bias vvpotentialwon thecontrol electrodes of the tubes l and 3; that is on one, Aor more, of the ampliier stages Ipreceding :the detector. The circuit is l.so arranged that an increasing signal, which proyduces a decrease.- in detector anode current, will lowerthe amplication'obtained from the preceding tube, ortubes, thus causing the signal reaching the detector to decrease.

:.By lproperly `proportioning the resistance R in rthedetector circuit, as well as its anode current, ,a gooddegree-of'control may be obtained. By makingthe resistance variable, the degree of Yautomatic control is varied. The potential drop acrossthe resistance R-has the polarity indicated across the capacityC. 1f the detector anode curvrentdrops, this potential decreases and the result .is-a greater positive potential on the pre-detector amplifier., control electrodes due to the sourcev V. Thus, the .1 amplication of these 'stages is decreased. The capacity of the condenser C should belarge enough to byvpass all necessary frequenciesraround the resistance R.

Furthermore, the anode potential B of the am- -plierstagesshould be not greater than 45 volts .because ofthe positivepotential on the control Aelectrodes .of the tubes. of these stages. It will, also, be noted that. the anode source used for the idetectorfstage lmust'be-:entirely separate from the vother source..used.iorsupplying anode potential being connected to. the lead 2 l. is also-connected to one terminal of the variable .not be `limited to. 45 volts.

for the other tubes, since it has the resistance R between its negative terminal and the cathode circuit.

In Fig. 2 there is shown a modication of the invention, embodied in the same type of circuit, although simplified to a greater extent, as shown in Fig. l. In this modification, the control electrode ci the pre-detector amplifier tube 3 is biased negativelyby asource 2Q, and this negative bias is varied in the saine manner as in the case of the positive system in Fig. l. In this -modification the positive terminal of the source 29 is connectedby a lead 2l to the cathode of the ,detector tube the vcontrol electrode of the latter The latter lead resistance R, the negative terminal of the source B1; and theopposite'terminal of the variable resistance R being connected by a lead 22 to the cathode of the pre-detector amplifier tube 11n. this modicationg'it is-not necessary to pros vide a separate source-of anode potential Brfor thedetector tube;Y in fact acornmon anode source lmay be used, but it is necessary vto provide'asep- .arate cathode; heating supply.v 23 for the'` cathode 3 ,of` the detector tube. iIf-the-indirect heater `type .of tube 4is usedrfor the detectorfand amplier tubes, -a common. heater supply is permissible .withthecathodes connected to the necessary .dif-

`ferentpoints vin the-circuit. ,However, due to the l `usefofa. negative -potentiallony the: pre-detector arnplirlerztubefi, or the tubef! which; is to'be understoodas omitted only. Vfor the sake -of sirnplicity, the anode potential for these tubes need Ii Vthe anode potential for tube 3 is higher than that desired for detector tube, theanode supply for tube may be tapped y.ofi ,at the necessarypoint along the'ano'de supply source. Y

,nthe modicationshown invFig. 2; the am- 'plication oi the pre-,detector stage, 'or stages; Vis

varied .by varying lthe .working-position along their grid potential-plate current curves,athus changing: the slope at #the working position. fW-hile- I. have `speeiiically shown an radio receiver hof. the tuned-radioffrequency type, it` isto be Vunderstood.- thatthe-'invention is not limited to `anyfparticular type ofrfpre-detector amplier, nor jtofamplierstagescoupledfasfshown in Figs. 1 and 2. These ampliierstages may be .of the radio frequencyA `type orifintermediate frequency type, andmay be'tunedL-or untunedf or'any of thev usual combinations of: these types.

Thus, ilnFigs. 3 andfi there are shownemodied `forrnsoi the-invention,fthe'gures showing the application .oithissame type of automatic volrune control tofa biastypeidetector. 'In'this case the source i? pr0vides-negativebias potentialfor the control-electrode Iof the detector tube 6. The action vci thecircuits shown in Figs. 3 and 4y is now. described. nFig B-,thesame cathodesource can .be used ifor detectorand radioirequency tube evenif these tubes are of .the lament type, vbut separate anodesupply sourcesmust be used. .The .anode current of the detector tube vincreases as the strength of theincorning. signal increases, and this causesarise in rthe voltage. drop produced across lthe resistor R. fThis potential adds to the negative bias-supplied by source 2i] in the control circuit of tube 3,thus decreasing theA amplica- 'tion of this tube,-as in the case shown in Fig. 2.

In Fig.' 4- ane arrangement using the bias type r`detector,appliedl.to -awcircuit is` shownin which v,the increasing. incoming signal causes-an increasing positive potential to be placed on the control electrode of tube 3. Its amplification is therefore decreased in the same manner as in the case of the circuit shown in Fig. 1. In the circuit of Fig. 4, the anode supply source can be common, or a portion of it can be common to both anode circuits, but the cathode supply sources must be separate for the two tubes if the lament type of tube is used. In Fig 4, the control electrode bias potential source 20 should be negative to a small degree only, so that the amount of potential produced across resistor R will be suflicient to `cause the control electrode of tube 3 to be positive to a relatively high value when a strong signal is received.

In order to enable those skilled in the art to more thoroughly design circuits embodying the invention, the following mathematical formul are utilized to elucidate the laws governing the phenomena taking place in the circuits.

In the formulae given below the following symbols are used to designate the various electrical values in the circuit:

Eg=Constant voltage supplied by xed source to control electrode of amplifier tube.

Vg=Necessary voltage on control electrode of amplier tube to bring amplification to lowest desired level.

vg=Necessary voltage on control electrode of amplifier tube to give maximum amplification.

R=value of resistor R in anode circuit of detector tube.

I=Normal anode current of detector tube with noincoming signal.

i=That change in detector anode current which accompanies the permissible uncontrolled increase in output signal intensity, and which is necessary in order to provide the controlling change in voltage drop across the resistor R.

The relation between the above symbols is giV en below for the four circuits described in Figs. 1 to 4.

For Fig. 1 Where vg is nearly zero, or slightly negative, and Vg is positive For Fig. 2 where Vg and vg are both negative For Fig. 3 where Vg and vg are both negative For Fig. 4 where vg is probably slightly negative, and Vg is positive Furthermore, it is to be understood that the anode and other voltage supply sources, which are shown by means of the standard battery designation symbol in the figures, can be interpreted as another type of supply source such as a socket power unit or motor generator without special mention of this in the text. While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. In combination, in a radio receiver, a radio frequency amplifier comprising an electron discharge tube provided with an input and output circuit, a current source for energizing the anode of the tube, means for normally positively biasing the control electrode of the tube, .a detector comprising an electron discharge tube having its input circuit coupled to the amplifier output, said detector being of the type including a leaky condenser in its grid circuit, a current source for energizing the anode of the detector tube, a common conductive path including an impedance connected directly between the low potential side of the last source and the cathodes of said tubes, and a conductive path connected directly between the low potential side of the biasing means and the low potential side of the impedance.

2. In combination, in a radio receiver, a radio frequency amplifier comprising an electron discharge tube provided with a signal input circuit and an output circuit, a current source for energizing the anode of the tube, means for positively biasing the control electrode of the tube, a detector comprising an electron discharge tube having a tuned input circuit coupled to the amplifier output circuit, a current source for energizing the anode of the detector tube, a common conductive path including an adjustable resistor connected directly between the low potential side of the last source and the cathodes of said tubes, and a conductive path connected directly between the W potential side of the biasing means and the low potential side of the impedance, said detector being of the leaky grid condenser type.

3. In combination in a radio receiver, means for collecting signal energy, said means being subjected to variations in local eld intensity, a stage of radio frequency amplication coupled to said collecting means and including an electron discharge tube provided with a control electrode, a cathode, and an anode, a detector stage coupled to the anode circuit of said `am plier stage, the detector stage including an electron discharge tube provided with an input circuit and output circuit and a leaky grid condenser in its input circuit, a source of positive biasing potential connected between the control electrode of said amplifier tube and the output circuit of said detector tube, and a variable resistor in the detector output circuit connected between the negative side of the biasing source and the cathodes of the amplifier and detector tubes for controlling the biasing action of said source on the amplier control electrode.

EDWARD T. DICKEY. 

